This invention relates to design improvements for catalytic reactors and other mass or energy transfer systems used to process liquid solutions or mixtures in the chemical industry, and particularly includes new designs for recirculating or so-called loop reactors incorporating honeycomb monoliths as essential catalyst-supporting or flow-regulating structures.
The chemical industry employs a wide variety of recirculating tank or batch reactors for chemically or physically processing chemical mixtures that include liquid solutions or mixtures, examples of specific reactor types including stirred tank, bubble column, and jet loop reactors. Many reactors of above mentioned type and of the prior art utilize solid catalyst granules or particles which are dispersed within a liquid medium comprising one or more reactants via stirrers or agitators, or via the addition of momentum through gas or liquid streams, to produce a product. When a gas is required to produce the product, it is usually fed into the reactor below the agitator, so that the agitator may also serve in the re-dispersion of large bubbles which may form in the reactor.
Although such stirred tank, bubble column, and jet loop reactors are usable for both continuous as well as for batch production, the catalytic particles experience continual attrition and must be separated from the reactant liquid to obtain the final product liquid. The required separation of the catalyst particles requires additional apparatus and operating procedures that add significant cost. Further, even with agitation, still zones with different hydrodynamic conditions exist and settling of the catalytic particles may occur.
Also, bubble size in a gas/liquid reactor is a strong function of the agitation produced. Often coalescence occurs, which produces larger bubbles, reduces gas/liquid mass transfer effectiveness, and yields unfavorable catalyst residence time distributions for the gas and sometimes the liquid.
One approach toward improving gas-liquid distribution in a tank reactor is shown in U.S. Pat. No. 4,234,650. In that patent, a gas is injected within a liquid jet into a large circulation tube within a reactor enclosure. The resulting gas/liquid mixture is then recirculated through and around the tube.
Structured or monolithic catalysts such as catalyst honeycombs offer the advantage of allowing for thin catalyst layers with high effectiveness factors and excellent mass transfer characteristics. However, as shown in U.S. Pat. No. 4,363,787, monolith use in the prior art typically involves fixed-bed, continuousoperation reactors. One variation on this approach, shown in Baltzer Science Publishers, August 1999, volume 3 (1999), page 35, circulates small moveable monoliths continuously through a reservoir of reactant liquid.
None of the prior art structured catalyst reactor designs have offered sufficient practical or economic advantages to displace any of the stirred tank, bubble column, and jet loop designs used for commercial processes. Thus the disadvantages attending the use of particulate catalysts in such reactors have not yet been overcome.
In view of the foregoing, the present invention provides an improved method and apparatus for transforming a chemical reactant into a desired product using a fixed catalyst. In particular, the invention provides improved recirculating catalytic tank reactors for processing a liquid medium (a mixture, solution, or suspension comprising at least one liquid phase) utilizing a monolithic honeycomb catalyst bed in combination with internal agitation flow means for circulating and recirculating a liquid comprising reactants and products around and through the channels provided within the honeycombs. The reactants and products may comprise single species or mixtures, and may be present in the liquid medium as dissolved or dispersed gases, liquids, or solids.
These recirculating reactors, hereinafter termed monolith loop reactors and including reactor types such as jet loop, stirred tank and bubble column reactors, produce the improved operational results such as controlled reactor behavior, excellent kinetic properties, and a high effectiveness factor. Moreover, the improved reactors do not have the problems related to catalyst handling associated with typical slurry reactors. Specifically avoided are problems relating to separation of the catalyst particles from the product stream, settling of the catalytic particles within the reactor, and continual attrition of the particles.
The loop reactors of the present invention include at least one honeycomb monolithic catalyst, formed of catalytic material or comprising a substrate with a suitable catalyst provided on surfaces thereof, fixedly positioned within the tank. At least one bypass passageway is provided adjacent the catalytic substrate, and internal agitator means are provided to recirculate liquid medium comprising reactants through the catalyzed flow channels of the monolith and about the monolithic substrate by means of the bypass passageway. Reactor designs for both two-phase (liquid-solid catalyst) and three-phase (gas-liquid-solid catalyst) chemical, biochemical and petrochemical processes are provided. Internal agitators for the liquid medium may comprise mechanical, liquid jet, or gas bubble agitators.
The reactor designs of the invention may also be adapted for use in other fluid processing applications, examples of such applications including adsorption, absorption, or extraction processes for promoting mass or energy transfer among any two or three of a liquid phase, a gas phase, and a solid material disposed on or in the honeycomb monolith. A useful liquid processing apparatus for such applications includes a suitable liquid containment vessel in which the honeycomb monolith is disposed, the honeycomb being positioned between upper and lower collection chambers in the vessel.
For these applications the honeycomb may or may not be provided with a catalyst or adsorbent, but in any case it will incorporate a plurality of parallel open channels connecting the upper and lower chambers. Also included within the containment vessel will be at least one by-pass conduit or passageway connecting the upper and lower chambers, that passageway providing a return path for the recirculation of gases and liquids in the vessel through the honeycomb. Again, energy for driving the recirculation may be supplied by mechanical, liquid or gas bubble agitation means such as a blade stirrer, gas sparger, liquid jet, or liquid jet/gas ejector system of the kind employed with jet loop reactors.